In recent years, we have seen a progressive movement of invasive procedural care from an inpatient to an ambulatory care model. There is already tremendous momentum behind this phenomenon, due, in part, to the potential to improve efficiency and to reduce the cost of care as well as the innovative appeal of new technology that enables procedures to be performed in a "minimally-invasive" manner. However, the rapid and progressive conversion of procedural care to an ambulatory setting can occur without a clear understanding of the safety implications, and without formal evaluation of the "'hidden" system-based risks associated with this practice model. As practitioners and researchers in this environment, we know that the system is complex. There are important interactions and interdependencies between components (staff, instrumentation, protocols, procedures, information, communication, and scheduling cycles) that further influence provider performance and patient safety. Given this exposure, we are clearly overdue for a formal analysis of the systems-based risks associated with ambulatory procedural care. What hampers our progress, however, is a general lack of experience and knowledge regarding the most appropriate approach to prospectively assess risk in such a complex socio-technical environment. In other high-risk industries such as the nuclear power, chemical engineering, environmental protection and telecommunications industries, experts have employed a number of powerful probabilistic modeling formalisms to help understand and manage systems based risks associated with both standard- and novel- operating conditions. Our proposed work will focus on the use of STAMP (Systems-Theoretic Accident Model and Processes) as a strategy for assessing and managing risk in the ambulatory care setting. STAMP was developed by researchers at MIT and is now being used widely to prospectively model risk in the aerospace and other high complexity/high risk industries where safety and performance are strongly influenced by socio-technical interactions. Our long term goals are to demonstrate the value of this STAMP approach to assess risk in complex socio-technical environments and to generalize its use to all clinical areas where human and organization factors play a significant role in safety and performance. As a first step, we will conduct a comprehensive prospective risk analysis using STAMP, focusing on ambulatory procedural care delivered in a large urban setting. [unreadable] [unreadable] [unreadable]